The proposed study will investigate the protective role of alveolar macrophages against Pseudomonas aeruginosa infection during bone marrow suppressive chemotherapy, and evaluate the cell mediated immune response of lung macrophages and lymphocytes to pseudomonas. This study will compare alveolar macrophage phagocytosis and bactericidal activity against pseudomonas in normal (non-immunized) dogs and in dogs actively immunized with pseudomonas lipopolysaccharide vaccine. It will also compare macrophage bactericidal activity against pseudomonas before cyclophosphamide-induced leukopenia and during leukopenia. The experimental design will use 2 pairs of dogs with at least 10 dogs in each pair. One dog of each pair will receive 6 i.m. injections of serotype 6 pseudomonas vaccine while the other dog will remain unimmunized. Prior to immunization both dogs of the pairs will be lavaged for collection of lung macrophages and lymphocytes. The cells will be tested for phagocytosis of pseudomonas, for migration inhibitory factor (MIF) activity, and for lymphocyte transformation activity. In addition, ultrastructural studies will be made of macrophages and B and T lymphocytes will be enumerated in lavage fluid and peripheral blood during treatment.